Harsh Chuggle, Surge, Miss, Hesitates W/History DTC P071
Group Ref.: Engine Fuel & EmissionsBulletin No.: 476506
Date: May, 1994
SUBJECT:
HARSH CHUGGLE, SURGE, MISS, HESITATION ACCOMPANIED BY A HISTORY DIAGNOSTIC TROUBLE CODE P071 (CHECK/REPAIR PER DTC)
MODELS:
1993 CADILLAC ALLANTE, ELDORADO COUPE AND SEVILLE SEDAN
1994 CADILLAC ELDORADO, SEVILLE AND CONCOURS
WITH 4.6L ENGINE (VINs Y AND 9 - RPOs LD8 AND L37)
CONDITION:
Some owners may experience engine roughness, harsh chuggle during highway driving, surge, miss and hesitation with no MIL or message and a History Diagnostic Trouble Code P071.
CAUSE:
Code P071 sets when there is a rapid change in MAP with no corresponding change in the TP sensor or rpm. A DTC P071 may be a symptom of a driveability condition such as backfire, stall, or loss of power. A falsely set DTC P071 may be caused by internal "noise" in some Northstar PCMs induced into the internal PCM MAP circuit.
NOTE:
Engine oil near or on map sensor Is a normal condition. MAP sensors should not be replaced if engine oil is present.
CORRECTION:
The Northstar's PCM has been redesigned to correct this internal circuit "noise" condition. To diagnose and repair the above conditions, perform the following procedures:
1. If the vehicle has multiple Diagnostic Trouble Codes and DTC P071, diagnose and repair the other diagnostic trouble codes first.
2. If there was a backfire or stall, diagnose that condition first.
3. If the vehicle is a 1993 and had a loss of power after an extended highway drive, perform the procedures outlined in Corporate Bulletin 216306 (GM of Canada 93-6-118; Cadillac 93T49).
4. If the vehicle is a 1993, perform the procedures outlined in Corporate Bulletin 316005 (GM of Canada 93-6-118; Cadillac 93T101).
5. If the vehicle has a harsh chuggle during highway driving, surge, miss or hesitation accompanied by a History DTC P071, inspect the service part number on the PCM. If it is one of the present service part numbers listed below, replace the PCM using one of the appropriate new service part numbers listed below.
6. If the PCM has the new service part number, follow the appropriate service information manual procedures for DTC P071 and inspect the MAP sensor connections and circuitry.
PARTS INFORMATION:
Parts are expected to be available on May 23, 1994.